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My input is that the interplanetary economy can include terraforming efforts, say the sulfur and CO2 removal from Venus can be exported to Mars for agriculture as sulfur and carbon content. A very wild imagination is that the silicon after exploitation of ores on Mars, near earth objects or asteroids, meteorites etc. can be split into nitrogen by nuclear reaction.
1 mole of Si28 + huge energy input from nuclear fusion or fission ---> 2 moles of N14.
Knightdepaix-
First of all, welcome to Newmars!
Iron can't be burned in a carbon dioxide atmosphere becuase CO2 likes to hold onto its oxygens more than Iron does.
Thank you for having me.
For the reaction between Fe and CO2, obviously under the Martian surface temperature range (-20° C to -132° C), CO2 is thermodynamically more stable then iron oxides. However, if some CO2 can be reduced to carbon monoxide, this CO loses oxygen to iron for that temperature range, which is why a reaction starter like silane is needed. The energy generated from reaction of Fe and CO splits more CO2 to CO and continues this late reaction. In essence, the reaction between Fe and CO in the temperature range produces energy for transportation use. More input if counter reasoning is ok.
I like the idea of molten salt too. As Martian atmosphere is almost CO2 and regolith is often iron oxides, how about using inorganic/ionic carbonate or organic orthocarbonate esters solvent or colloid of both as the molten salt ? Because of lower Martian temperature range, salt with a higher temperature liquid phase like table salt is not sought after as much as on Earth. Native sodium and chloride are harder to find than iron, silicon, aluminum and CO2 anyway. On the other hand, ionic carbonate decomposes to oxides and CO2 on earth upon heating, lower Martian surface temperature decreases the chance of that decomposition during machine operation. In essence, find an organic orthocarbonate or orthosilicate ester colloid with ionic iron carbonate, obviously the liquid phase of that orthoester itself shall lie within Martian surface temperature range. Such colloid would separate into gaseous orthoester and solid iron carbonate if more heat input into the system of molten salt, useful for maintenance. In worse case and accident scenario to machines, the orthoester and iron carbonate decompose to solid iron oxides, gaseous ether and carbon dioxide. Because of the absence of oxygen and ether not reacting with CO2, both gases escape to atmosphere without further harm.
I imagine such colloid as blood, where iron compounds flow in blood plasma. Conducting electricity and acting as buffer are great advantages for such colloid; obviously more additives can be desired in that colloid, just like glucose and ions in blood.
Just a small input from myself.
CO2 can be compressed into dry ice and then transform into some kind of polymer for storage. Sulfur itself can exist as orthosulfur allotrope but much energy is needed to reduce sulfur acid to sulfur. However if such reduction is given a go, the water and oxygen generated can be recycled for use, say in the space industrial station where all these reaction take place. Both CO2 polymer and sulfur can then be exported to another planet, say Mars where human or plant immigration happens concurrently.
Adding more to carbonyl metallurgy, iron, nickel or transition metal carbonyls are useful because they change phase under relatively mild but high temperature, which is useful for molding. To extract metal from ore, hydrochloric acid (or sulfuric acid for that matter but sulfate can be reduced to sulfide, wasting carbon or carbon monoxide designated for metallurgical use) can be used to leach the metals as metal chlorides, leaving silicon and titanium oxides. The metal chlorides solution are converted to oxides, metal by metal and regenerating HCl acid. Each metal oxides is then reduced with hugely excess carbon monoxide, not carbon; this late process generates carbon dioxide which can be splitting into carbon monoxide for recycling use or released to atmosphere. The amount of CO not used for reducing iron oxides react to form iron pentacarbonyl which is drained away from reaction vessels. Any residues of iron (or transition metals for that matter) or CO can be oxidized by native perchlorate into metal chloride and CO2 which are both treated as mentioned.
For native source of HCl acid, also look into perchlorate.
What made wood, coal, whale oil, and petroleum oil feasible and economic to use on Earth was our oxidizing atmosphere. By far, the largest massflow through any sort of combustion device is the oxidizer. All we had to do was find a fuel.
It's not like that on Mars: the atmosphere is inert. You have to find or create both fuel, and the far-more-massive oxidizer. I have my doubts about combustion engines ever proving to be truly practical there, precisely because of that problem.
Using silanes or boranes are remedying that issue as they burn in CO2; however, can iron filling also burn in CO2 ? Say a small amount of silane mixture or solution (a liquid, details below) as a fire starter reacts with CO2 to drive the reaction between Fe and CO2, which releases more energy until all Fe filling is burnt. According to the Ellingham diagram, iron can reduce carbon dioxide to carbon while oxidizing itself to the thermodynamically stabler iron oxides. The iron oxides and carbon products can be dumped onto the ground: the Martian regolith is mostly composed of iron oxides anyway. The carbon can be recycled. In essence, the iron filling is "coal" on Mars.
Or if liquid fuel is needed, how about picking a silane/organic solvent solution with a broad liquid phase that mostly lie within the temperature range on Mars surface. Say some ionic iron or silicon hydride salts (for example Mg2FeH6 magnesium iron hexahydride) in a diethylsilane (m.p. −132 °C, b.p. 56 °C all under earth atmospheric pressure) and hydrogen/silane solvent suspension.
As a note, if Mg2FeH6 can be made, could something like MgSiH6 also be made ?